来自学弟的问题：一个vector>>v, 写一个模板函数Size()， 然后可以直接auto [n,m,k] = Size(v)获取这个高维矩阵的各维维度？

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#include#include#include#include 

using std::vector;

templatestruct Dimension {static constexpr std::size_t value = 0; };
templatestruct Dimension>{static constexpr std::size_t value = 1 + Dimension::value; };
templateinline constexpr size_t dim = Dimension::value;

template>std::arrayshape(const T & a)
{std::arrayresult{a.size()};
    if constexpr (N>1) {auto sub = shape(a[0]);
        std::copy(sub.begin(), sub.end(), result.begin()+1);
    }
    return result;
}


#define assert_eq(a, b) assert((a) == (b))

int main() {static_assert(dim== 0);
    static_assert(dim>== 1);
    static_assert(dim>>== 2);
    static_assert(dim>>>== 3);

    {//        assert_eq(shape(1), (std::array{})); // compile error
    }
    {vectorb = {1, 2, 3};
        assert_eq(shape(b), (std::array{3}));
    }
    {vector>c = {{"a", "b", "c"}, {"c", "d", "e"}};
        assert_eq(shape(c), (std::array{2, 3}));
    }
    {vector>>d = {{{"a", "b", "c"}, {"c", "d", "e"}},
            {{"a", "b", "c"}, {"c", "d", "e"}},
        };
        assert_eq(shape(d), (std::array{2, 2, 3}));

        auto [a, b, c] = shape(d);
        assert_eq(a, 2);
        assert_eq(b, 2);
        assert_eq(c, 3);
    }
}

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